Electron tube with inert oxide coating on the envelope



July 4; 1967 3,329,854

ELECTRON TUBE WITH INERT OXIDE comma ON THE ENVELOPE HIROHIDE MIWA ETAL Filed March 5, 1965 PIP/004.07

United States Patent M 3,329,854 ELECTRON TUBE WITH INERT OXIDE COATING ON THE ENVELOPE Hirohide Miwa and Takamasa Shiojiri, Akashi, Japan, assignors to Kobe Kogyo Corporation, Kobe, Japan, a company of Japan Filed Mar. 5, 1963, Ser. No. 263,012 Claims priority, application Japan, Mar. 17, 1962, 37/ 10,745 6 Claims. (Cl. 313-318) This invention relates to electron tubes and envelopes therefor and more specifically to a novel and improved discharge tube such as the Geiger-Muller counter tube and the like.

In the manufacture of electron tubes and particularly discharge tubes such as the halogen-filled Geiger-Muller (G.-M.) tube, it is desirable to use materials such as metal alloys and the like within the tube that will not react materially with the halogen. Examples of materials presently used in halogen-filled tubes are chromium-iron alloys, platinum, tin oxide and the like, for both the tube elements as well as the lead-in wires which are sealed in the tube wall. The chromium-iron alloy is attacked to a material extent by the halogen, and accordingly, very small portions can be tolerated within the tube. Platinum, while chemically stable, is exceedingly expensive, and tin oxide while exhibiting a strong resistivity to halogen presents considerable difiiculty in making electrical connections thereto. It is evident therefore that in the manufacture of G.-M. tubes utilizing the foregoing metals and oxides that the rejection rate is necessarily high, and the manufacturing process is both complicated and expensive.

This invention overcomes the disadvantages heretofore encountered in the manufacture of G.-M. tubes and provides a discharge tube having an air-tight envelope which does not require complicated manufacturing processes and which at the same time will assure dependable, lowresistance connections with the elements within the tube and permit the use of materials within the tube having high resistivity to chemical reaction with halogen.

Another object of the invention resides in the provision of a novel and improved discharge tube and method of manufacture.

Still another object of the invention resides in the provision of a novel and improved method for manufacturing an air-tight container with conductive elements extending through a wall of the container.

The above and other objects and advantages of the invention will become more apparent from the following description and accompanying drawings forming part of this application.

FIGURE 1 is a cross-sectional view of a conventional halogen-filled G.-M. tube.

FIGURE 2 is a cross-sectional view of a halogen-filled tube in accordance with the invention.

Referring now to the drawings, FIGURE 1 illustrates a known G.-M. tube having an outside envelope 1, a conventional stem 2 with lead-in wires 3 of a relatively high chromium-iron alloy, a platinum wire 4 connected to one of the lead-in wires 3 and bonded to a tin oxide film 5, and a central electrode 6 of a high chromiumiron alloy. It will be observed that a relatively small amount of the chromium-iron alloy is disposed Within the tube, and accordingly, the reaction with the halogen gas is minimized. The film which extends about the periphery 0f the envelope is formed of tin oxide which has a high resistivity to the halogen gas.

A relatively small piece of platinum wire 4 is utilized to connect one of the lead-in wires to the tin oxide film. It is exceedingly diflicult, however, to join the platinum Wire to the tin oxide film, and this difficulty accounts in 3,329,854 Patented July 4, 1967 part for a relatively high rejection rate in the manufacture of the tube.

An improved tube in accordance with the invention is illustrated in FIG. 2, which overcomes the difficulty heretofore encountered and provides a structure that is relatively easy to manufacture, has an exceedingly low rejection rate and avoids the difficulties encountered in the utilization of conventional procedures in providing leadin wires and internal connections. More specifically, the structure of FIG. 2 has a glass envelope 7 which may be cylindrical in configuration and provided with a single closed end portion 7'. A peripheral electrode 8 formed on both the inner and outer surfaces of the envelope 7 is preferably formed of tin oxide which is carried over the edge of the open end portion of the tube so that the internal and external layers of tin oxide are electrically connected. A central electrode 9 is formed of a ceramic rod that is entirely coated by tin oxide film, and a ceramic disc or base member 10 closes the open end of the envelope 7 and has a central opening through which the ceramic rod 9 extends.

A preferred composition for the glass envelope has a softening point in the general range of 550 centigrade to 600 centigrade and is formed of the following materials:

Percent SiO 68 N320 CaO 5 MgO 3 E203 3 A1203 and FO3 3 The ceramic base member 10 may be formed of the following materials:

Percent A1 0 95.8 SiO 2.8 Other 1.4

The bonding material 11 for bonding the envelope in a cooperating recess in the base member 10 and for sealing the ceramic rod 9 in the central opening of the base memher is preferably a low-melting point glass or bonding glass-ceram which permits it to be heated to a welding temperature without deforming either the glass envelope 7 or the electrode 9. One satisfactory composition for a low-melting point bonding glass is as follows:

Percent PbO 7 1.5 B 0 9 SiO 14 Nazo 2 A1 0 2 ZnO l The foregoing composition has a softening temperature in the range of 350 C. to 400 C. and accordingly, will elfect a bond between the base member 10, the electrode 9 and the envelope 7 without damaging any of the elements.

In the manufacture of the tube as illustrated in FIG. 2, the glass envelope 7 and the ceramic electrode 9 are first formed and are then heated to a temperautre of about 500 C. A solution comprising approximately grams of tin chloride 50 cc. of water, 10 cc. hydrochloric acid, 0.25% to 5% antimony trichloride and 30 cc. ethyl alcohol is mixed and discharged in a fine spray onto the surfaces of the envelope and electrode. The high temperature produces a reaction causing the tin chloride to decompose and produce a thin layer of a tin oxide adhering strongly to the surfaces of the envelope and the electrode. It will be observed that during the process, both the inside as well as the outside of the envelope are coated, and the entire surface of the electrode is coated as indicated at 8'.

In practice, solutions of the other salts can be used in place of the metal salts mentioned above, as, for instance,

(1) .Tin chloride and antimony chloride (2) Tin chloride and indium chloride (3) Cadmium chloride and indium chloride The resultant oxide film formed on the envelope and electrode is exceedingly stable in the presence of halogen gas, can stand a high temperature, and forms a dense, strong and very thin conductive layer having a transparent appearance.

Having prepared the envelope and electrode, the lowmelting point bonding glass is first ground into a particle size of about 200 mesh and is then mixed with an organic solvent, as, for instance, isoamyl acetate (CH CO C H to form a relatively thick paste. The coated envelope and electrode are then assembled in the stem as illustrated in FIG. 2, and the bonding material is inserted in the manner shown in this figure. The entire assembly is then heated to approximately 420 C. to melt the bonding material 11. After the completed tube has cooled to a normal temperature, the bonding material solidifies and forms an airtight bond with the coatings on the envelope 7, the stemtld and the coating on the central electrode 9. Inasmuch as the softening temperature of the glass envelope 7 and electrode 9 are well above the melting temperature of the bonding material, there is no deformation of these elements during the bonding process.

Another important advantage of the structure as described above resides in the fact that when performing the bonding operation, the metal oxide does not dissolve into the glass upon being heated. This presents a substantial advance in the art of sealing electron tubes and particularly in cases wherein a metal oxide film is carried on the surface of one of the elements being bonded. It is believed that in prior bonding processes, the tin or other metal oxide upon being heated diffused into the glass and an intermediate layer was produced having different thermal expansion properties and thus resulted in material distortion and even cracking of the elements being joined. With the invention, however, it has been found that With the utilization of the materials as discussed, there is no impairment of the oxide films, the resultant structure is not distorted or cracked, and it has further been found that excellent conductivity of the film through the bonding portion is maintained. Inasmuch as the metal oxide coating on the inside of the envelope 7 is connected directly with the metal oxide coating on the outside of the envelope and further since the metal oxide coating on the electrode 9 extends through the electrode bond, any suitable means may be utilized in making external electrical connections to the tube and thereby avoiding the difiiculties heretofore encountered with structures such as that shown in FIG. 1 of the drawings.

From the foregoing, it is evident that electron tubes may be fabricated utilizing conductive oxide films to form the lead-in elements as well as the tube elements and which film can be used without encountering any deterioration or damage when bonding the stem of the tube to the envelope. It is also to be understood that the invention may be applied to tubes other than the discharge tube described above.

While only certain embodiments of the invention have been illustrated and described, it is apparent that alterations, modifications and changes may be made without departing from the true scope and spirit thereof as defined by the appended claims.

What is claimed is:

1. An electron tube comprising an envelope having an open end, a high temperature conductive oxide coating on and permanently bonded to the inner and outer surfaces and about the edge defining said open end to form a continuous coating, a base member closing said opening and a low temperature melting point bonding material having a melting point substantially below the melting point of said envelope and oxide coating and hermetically sealing said base to said oxide film, said oxide coating maintaining its relatively low conductivity and facilitating attachment of a lead wire thereto.

2. An electron tube comprising an envelope having an open end, an oxide coating on at least part of the inner, outer and end surfaces to form a continuous coating, a base member having a central opening for closing said open end, an oxide coated elect-rode Within said envelope and adapted to extend outwardly through said base member, and a low melting point bonding material hermetically sealing said base member to said envelope and hermetically sealing said electrode in the opening of said base member with a portion of said electrode extending within said tube, said oxide coatings having a relatively low conductivity and facilitating attachment of lead wires thereto.

3. An electron tube according to claim 2 wherein said oxide is a relatively inert metal oxide.

4. An electron tube comprising an open-ended envelope formed of a material containing oxides of silicon, sodium, calcium, magnesium, boron, aluminum and iron, a metal oxide coating on the inner, outer and end surfaces of said envelope, a base member closing said opening and being formed principally of oxides of aluminum and silicon and a low melting point bonding material bonding said base to the oxide coating on said envelope, said bonding material being formed of oxides of lead, boron, silicon, sodium, aluminum, zinc and cobalt.

5. An electrontube according to claim 4 wherein said envelope has a softening point in the general range of 550 C. to 600 C. and said bonding material has a melting point in the general range of 350 C. to 400 C.

6. An electron tube comprising an envelope having an open end, a base member having a central opening, said base member being sealed to the open end of said envelope, and an oxide coated electrode extending through said central opening and into said envelope and a low melting point bonding material hermetically sealing said electrode in said base member with a portion of the coated electrode extending externally of said base member said bonding material hermetically bonding the oxide coating to the Wall of said central opening;

References Cited UNITED STATES PATENTS 2,154,278 4/1939 Mouromtsefi 3133 17 2,899,582 8/1959 Hermsen et al. 31393 3,065,291 11/ 1962 Rexer 174-5064 3,207,938 9/ 1965 Anton 31393 FOREIGN PATENTS 876,123 5/ 1953 Germany.

JAMES W. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistam Examiner. 

1. AN ELECTRON TUBE COMPRISING AN ENVELOPE HAVING AN OPEN END, A HIGH TEMPERATURE CONDUCTIVE OXIDE COATING ON AND PERMANENTLY BONDED TO THE INNER AND OUTER SURFACES AND ABOUT THE EDGE DEFINING SAID OPEN END TO FORM A CONTINUOUS COATING, A BASE MEMBER CLOSING SAID OPENING AND A LOW TEMPERATURE MELTING POINT BONDING MATERIAL HAVING A MELTING POINT SUBSTANTIALLY BELOW THE MELTING POINT OF SAID ENVELOPE AND OXIDE COATING AND HERMETICALLY SEALING SAID BASE TO SAID OXIDE FILM, SAID OXIDE COATING MAINTAINING ITS RELATIVELY LOW CONDUCTIVITY AND FACILITATING ATTACHMENT OF A LEAD WIRE THERETO. 